Conventionally, in a mobile communication system, a radio control station is configured to determine a transmission rate of uplink user data, and to notify, to a base station and a mobile station, the determined transmission rate of uplink user data, by using a message of a layer 3 (RRC: Radio Resource Control layer), when setting a dedicated channel. After the setting of the dedicate channel, the radio control station is configured to control, depending on a change, of a status, the transmission rate of uplink user data.
In the case of data communication in particular, burst traffic may be caused with a higher probability than in the case of voice communication or video telephone communication. Thus, a high-speed change of a transmission rate has been desired.
However, a radio control station controls a great number of radio base stations, and thus a high-speed change of a transmission rate (e.g., about 1 to 100 milliseconds) is difficult from a viewpoint of a processing load and a processing delay for example. It may cause a risk of a significantly increased cost for an apparatus and cost for an operation of network lines to overcome the processing load and the processing delay.
Due to the above reason, the conventional mobile communication system has changed the transmission rate of uplink user data on an order of a few hundreds of milliseconds to few seconds. Specifically, when burst-like uplink user data must be transmitted as shown in FIG. 1(a), either of the methods shown in FIGS. 1(b) or 1(c) has been used.
The method shown in FIG. 1(b) is a method to provide a low transmission rate of uplink user data, whiling permitting a long delay and a low transmitting efficiency.
The method shown in FIG. 1(c) is a method to secure a resource (radio resource and hardware resource of radio base station) required for a high-speed transmission, and to provide a high-speed transmission rate of uplink user data, while permitting waste of a resource of an available time.
As described above, any of the methods has not been sufficient. Thus, a method for appropriately controlling a transmission rate of uplink user data while effectively using a radio resource has been discussed in the 3GPP and the 3GPP2 as international standardization organizations for the third generation mobile communication system.
Specifically, in a discussion which is called as the “Enhanced Uplink”, the “Dedicated rate control” and the “Common rate control” have been suggested as a method for controlling a transmission rate of high-speed uplink user data in a layer 1 and a MAC sub layer between a radio base station and a mobile station.
The “Dedicated rate control” is a method wherein a radio base station determines, per a certain timing, transmission rates of uplink user data of the respective mobile stations, and notifies the respective mobile stations of the transmission rates by a general common channel (SCCPCH: Secondary Common Control Physical Channel).
The mobile stations transmit uplink user data at the determined transmission rates. The radio base station may always give all mobile stations connected to the radio base station transmission opportunities, or also may give some of the mobile stations transmission opportunities in turn.
Generally, a radio base station uses an UP/DOWN/KEEP command so as to change the transmission rate of uplink user data of a mobile station. However, a countermeasure by using this method to solve a problem (e.g., accumulation of received erroneous commands) also has been reported (e.g., see Non-patent Publication 1).
The “Common rate control” is a method wherein a radio base station notifies, as information common to mobile stations having communication, a transmission rate of uplink user data or information required for the calculation of the transmission rate (hereinafter referred to as “transmission rate information”).
Based on the received transmission rate information, the respective mobile stations determine the transmission rate of uplink user data. The “Common rate control” can be realized, for example, by setting identifiers “Common” showing all users existing in a plurality of cells to the UE-ID (User Equipment-ID) to be set to the SCCPCH.
Another method has been suggested by which a total transmission rate common to the respective cells is periodically updated and is transmitted in the SCCPCH, and a share of a transmission rate of uplink user data of each mobile station is transmitted in a dedicated channel, so that a radio resource can be effectively used (e.g., see Non-patent Publication 2).
(Non-patent Publication 1) 3GPP TSG-RAN WG1 R1-030709
(Non-patent Publication 2) 3GPP TSG-RAN WG1 R2-041729
However, any of the conventionally suggested methods for controlling a transmission rate of uplink user data has used the SCCPCH. Since the SCCPCH can be flexibly used for various applications, a tendency is caused in which a great number of overheads (e.g., Transport Format Combination Indicator (TFCI)) are added.
Due to this reason, the SCCPCH has been further added with control data for the control of a transmission rate of uplink user data (e.g., setting of the identifier “Common” to the UE-ID) to cause an increased downlink transmission power, thus causing a risk of a restricted downlink capacity.
In the case where a priority class is provided in particular, a need to transmit transmission rate information for every priority class by the SCCPCH has been caused, thus causing a risk of a further increase of a downlink transmission power and a further restriction of a downlink capacity.
Furthermore, the SCCPCH uses a turbo code and a convolutional code. Thus, transmission rate information could not include higher-order bits and lower-order bit having different qualities. Thus, when a bit error is caused, an increased error may have been caused between the information and correct transmission.